In bone surgeries such as those for effecting fusion of bones (i.e., fusion and unification) after bone fracture, e.g., fusion of repositioned bones after spinal fracture, or following bone grafting, it is necessary that the relevant bones be kept tightly held together until their fusion is accomplished lest they should be displaced. In order to keep holding them together, steel wires have long been used, along with, depending on a given situation, a variety of devices such as metal rods, hooks, bolts (pedicle screws) and the like. From a standpoint, however, of avoiding the risk of spinal cord injury caused by the tips of the steel wires that could be created by fracturing during or after a spine surgery, use of metal fiber-made cables or cables made of high-strength synthetic fibers, such as ultra-high molecular weight polyethylene (referred to collectively as “bone-tying cables” in the present invention), has been becoming popular instead of steal wires.
In a surgery employing bone-tying cables, as FIG. 1 schematically illustrates the procedure of tying according to a typical manner using one of the above-mentioned cables made of synthetic fibers, bones to be held together (shown as round bars) are first tied with a loop of a bone-tying cable (together, if necessary, with a rod, a hook or the like as a splint), and then,
(1) while the knot (provisional knot) shown in FIG. 1(f) being supported, the two arms of the cable extending from it are held together and pulled tightly so that the size of the loop is reduced and the bones are fastened to each other, and, when the tension of the loop has been increased up to a required level, the knot is immobilized in the situation with, e.g., an adhesive or an attachment, or
(2) a provisional knot is formed from the situation depicted in FIG. 1(g) by pulling the two arms by hand in the directions indicated with the arrowheads, and, the two arms of the cable extending therefrom are then pulled firmly in both lateral directions, so that the size of the loop is reduced and the bones are fastened to each other, and, when the tension of the loop has been increased up to a required level, the knot is immobilized, with the tension being retained, by means of additional knots or an adhesive or the like, as required to prevent it from slipping. The above fastening process using the bone-tying cable must be a process in which a strong tension (e.g., 5-10 kgf) is created in the cable forming the loop. In order to overcome the frictional force between the fibers of the cable within the provisional knot, thereby causing them to slip with one another and thus reducing the size of the loop to achieve such a strong tension in it, the two arms extending from the provisional knot must be pulled with a force which will creates a greater tension in both of them. A device to enable this is known and has been produced by the applicant of the present application, with which the two arms of the bone-tying cable extending from the provisional knot are separately held and pulled (see Patent Document 1). With this device, fastening is performed by first putting the tip of the device against the provisional knot, then holding the two arms of the cable extending from the provisional knot separately with different structures at different positions, and pulling them rearward. With this device, however, unless the forces with which to pull the two arms are constantly adjusted to be equal, the provisional knot is likely to slip away from the tip of the device. Thus there was a room with this device for some improvement for easiness of operation.
Devices improved in this respect have been developed by the applicant of the present invention, which devices are; a bone-tying cable tightening device which is so made as to allow pulling the both arms of the bone-tying cable extending from a knot together as a bundle through a slit provided at the tip of the device (see Non-Patent Document 1), and a bone-tying cable tightening device which is so made as to once separate the cable's two arms in lateral directions and then hold and pull them together as a bundle, and which includes a trigger coupled with a ratchet mechanism enabling easier tightening of the cable, and is provided with a tension-adjusting mechanism for adjusting the tension applied to the cable (see FIGS. 2, 4, 5 and Non-Patent Document 2). And both are used in medical facilities across the country under the commercial names of “Tighting Gun [MH]” and “Tighting Gun [NTG], respectively. The latter device, for example, is provided, at the tip of its rod-like member 4, which extends forward from a grip portion 3, with a pair of projections as a knot-supporting means 5 extending in one lateral direction (on the left side relative to the forward direction, i.e., on the near side in the figures), and includes a sliding block 6 which is mounted, slidably in the longitudinal direction, around the rod-like member 4, wherein the sliding block 6 includes a guide projection 7 projecting in a lateral direction (on the left side relative to the forward direction, i.e., on the near side in the figures) and having a smooth cylindrical side face. On the sliding block 6 and closely above the guide projection 7, a pair of projections 8, 9 projecting also in the lateral direction (projection 8 is fused to and united with the guide projection 7) are provided, defining between then a space 10 through which the cable is allowed to pass in the vertical direction. In its cross section, the space 10 widens upward in a V-shape manner, and, to match the shape of the cross section, a transverse groove 11, which also widens upward, is defined in the upper part of the sliding block 6. Above the sliding block 6, a bar-like locking member 12 is supported by a pivotable arm 13, and the locking member 12 can fit with its side faces between the pair of projections 8, 9 and also within the transverse groove 11. The arm 13 is journaled on the sliding block 6 on the side opposite to the knot-supporting means 5 (on the other side of the sliding block 6 in the figures), and is biased upward with a spring so that the locking member 12 may be brought away from the space 10 and the transverse groove 11. In the grip portion 3, there is provided a drum, which is rotated stepwise in a fixed direction by a ratchet mechanism in response to pulling of a trigger 14. A pull cable 15, which is secured at one end of it to the drum, is secured at its other end to the rear face of the sliding block 6, and the device is so made that when the trigger 14 is repeatedly pulled, the sliding block 6 is forced to slide and retreat along the rod-like member 4. Further, the rod-like member 4 is supported by the grip portion 3 in such a manner that a rearward slide of the rod-like member 4 is allowed, with its rear end being connected to a tension-adjusting knob 17 which is equipped with a screw mechanism.
This device is used in the manner as schematically illustrated in FIGS. 3 and 4. Briefly, the device is held with a dominant hand, and while putting the knot-supporting means 5, which projects in the lateral direction from the rod-like member 4, against the provisional knot 21 of the cable which ties the bones 20 to be fastened. The two arms 22, 23 of the cable are separately hooked by the other hand on the upper and lower sides of the knot-supporting means 5, and then the both ends of the arms are held together and pulled in the proximal direction along the side face of the rod-like member 4 (FIG. 3(h)). Then the arms of the cable are hooked on the guide projection 7 to make a turn upward while being kept tense, and then, after being passed through the space 10 between the pair of projections 8, 9, they are hooked on the locking member 12, which is lifted above the sliding block 6 (FIG. 3(i)), and wound once about it (FIG. 3(j)). By pulling the trigger 14 a few times to pull the pull cable 15 and thereby making the sliding block to retreat, the locking member 12 is pulled down into the space 10 between the projections 8, 9 and also into the transverse groove 11. Thus, the two arms 22, 23 of the cable wound about the locking member 12 are securely held in position clamped between the V-shaped slopes of the space 10 and the both side walls of the transverse groove 11 and the locking member 12. Then, by repeated pulling of the trigger 14, the sliding block 6 gradually retreats in the rearward direction, and the two arms 22, 23 of the cable are pulled tightly, which, causing the cable to slip within the provisional knot, reduces the size of the loop and thereby firmly tie the bones to be fastened. At the very moment when the tension goes up beyond a predetermined level which has been set with the tension-adjusting knob 17, the rearward pressure from the sliding block 6, which is received by the rod-like member 4 at the knot-supporting means 5 via the two arms 22, 23 of the cable, overcomes the repulsive force of the spring which has been adjusted with the tension-adjusting knob 17, and the rod-like member 4 thereby slides slightly rearward for the first time. This movement is detected, e.g., through a window 25. Thus, after it is known that the predetermined strength of tension is achieved, a release lever 26 is moved to release the ratchet, thereby allowing the sliding block 6 to slide forward and loosen the two arms 22, 23 of the cable, which are then removed from the device. Though, in this situation, the knot is tightly fastened and will not easily return to its previous state, it is also possible to add one or more extra knots, to bond the knot with an adhesive, or to fix the knot with an attachment, for securer fixation of the knot.
While this device enables one to fasten target bones with required strength of tension and thus is widely used, it still have a room for improvement with respect to easiness of operation. For the device is unstable at the tip and somewhat readily fluctuates sideways and back and forth due to unsteadiness of the hand during the process in which the two arms of the cable extending from a provisional knot are held together and hooked on the guide projection 7, made to turn upward and then wound around the locking member 12. Therefore, in the case of a surgeon who is not accustomed to the handling of the device, the knot-supporting means 5 sometimes moves away from the provisional knot unless he handles the device with sufficient care, thereby making it necessary to carry out the process once again from the step where the tip of the device is put against the provisional knot. This has sometimes been troublesome for surgeons, who have to smoothly perform the surgery, in which there are often cases where fastening must be given at multiple points. Therefore, a device which is easier to handle has been needed with which factors causing to such unsteadiness of hand are reduced.    [Patent Document 1] Japanese Patent No. 3074205    [Non-patent Document 1] Pamphlet of “Tighting Gun [MH]”, Medical Device Approval No. 12BZ0286, Alfresa Pharma Corporation, Revised in October, 2004.    [Non-patent Document 2] Pamphlet of “Tighting Gun [NTG]”, Medical Device Approval No. 12BZ0286, Alfresa Pharma Corporation, Revised in October, 2004.